Motor driven drilling hammer

ABSTRACT

The invention concerns a motor-driven drilling hammer with percussion and rotary drive, and a drill sleeve ( 14 ) which is disposed in a housing and is drivingly connected to a tool or a chuck for receiving the tool. In order to improve vibration damping, the drilling hammer is designed such that the drill sleeve ( 14 ) is connected on its outer periphery ( 30 ) to a spring means ( 32 ) of an elastomeric material ( 34 ) which has a wall thickness of 1 to 10 mm, and wherein the spring means ( 32 ) holds a damping mass ( 36 ) which can be deflected relative to the drill sleeve ( 14 ) in the peripheral direction and in the longitudinal direction ( 20 ) of the drill sleeve ( 14 ) due to the elasticity of the spring means ( 32 ), thereby effecting damping and reduction of vibration.

This application claims Paris Convention priority of EP 05 024 979.6 filed Nov. 16, 2005 the complete disclosure of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The invention concerns a motor-driven drilling hammer with a percussion and rotary drive, and a drill sleeve which is disposed in a housing.

One problem of drilling hammers is that the percussion drive causes strong vibrations transferred from the percussion mechanism to the housing and handle components. It has been proposed to provide a demolition hammer with a spring/mass system, wherein the oscillations caused by the axially operating percussion drive are damped by a mass which is pretensioned on both sides by springs.

It is the underlying purpose of the present invention to effectively reduce vibrations in drilling hammers.

SUMMARY OF THE INVENTION

This object is achieved with a drilling hammer of the above-mentioned type in that the drill sleeve is connected on its outer periphery to a spring means of an elastomeric material which has a wall thickness of 1 to 10 mm, wherein the spring means has a damping mass which can be displaced in the peripheral and longitudinal directions of the drill sleeve relative thereto due to the elasticity of the spring means, thereby effecting damping to reduce vibrations.

In the inventive drilling hammer, the damping mass may oscillate in a translatory and also rotary direction. The spring/mass system is thereby designed, such that oscillation of the damping mass in the translatory and rotary directions is, in each case, counter-phased to the oscillations of the drill sleeve, such that these oscillating frequencies are cancelled or effectively damped. This reduces the overall oscillation excitation of the drilling hammer by these two main components. In accordance with the invention, it has turned out that, especially for small and medium-sized drilling hammers, the vibrations at the handle are primarily generated by the percussion and rotary forces acting on the tool. Since the percussion and rotational speed of drilling hammers remain largely constant during operation, the oscillations can advantageously be damped to reduce vibrations. The inventive design reduces vibrations in a highly effective fashion, since translatory and also rotary oscillations can be damped.

The inventive arrangement of the damping mass permits cancelling of at least two dominant excitation frequencies by one single mass. The design of the spring/mass system depends on the geometry and weight of the damping mass, and the geometry and design of the elastomeric spring means. In order to reduce e.g. the damping frequency, the elastomeric mass may be thicker or the weight of the damping mass may be increased. This must be achieved in each case through suitable design of the spring/mass system in correspondence with the frequencies to be damped, which are generated during operation of the drilling hammer.

With particular advantage, the elastomeric material may continuously surround the drill sleeve in the peripheral direction, and be substantially cylindrical. This produces a very load-resistant connection between the damping mass and the drill sleeve, which is also largely insensitive to shearing loads. In certain cases, it may also be advantageous to segment the elastomeric material, i.e. to provide several bordering or spaced-apart segments of elastomeric material on the outer periphery of the drill sleeve or to provide the elastomeric material with perforations, recesses or openings in a radial, tangential or axial direction.

For the use of small and medium-sized drilling hammers, a wall thickness of the elastomeric material of 4 to 8 mm has proven to be advantageous. In one further preferred embodiment, the elastomeric material has an axial extension in the longitudinal direction of the drill sleeve of 5 to 20 mm.

The damping mass may moreover advantageously be substantially cylindrical. This yields a symmetric mass distribution which is uniform and continuous in the peripheral direction around the drill sleeve, which is suitable in view of vibration damping. The axial extension of the damping mass may advantageously also be 5 to 20 mm. It is preferably 3 to 8 times its wall thickness.

The damping mass/spring system is moreover advantageously designed to damp vibrations of between 30 and 100 Hz. For smaller drilling hammers, the oscillations to be cancelled are preferentially between 70 and 80 Hz.

Further features, details and advantages of the invention can be extracted from the enclosed claims, the drawing and the following description of a preferred embodiment of the inventive drilling hammer.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows a sectional view of a relevant region of a drilling hammer; and

FIG. 2 shows a perspective view of the drilling hammer according to FIG. 1, illustrating the rotary drive of the drill sleeve.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The figures show a region 2 comprising the drive components of an inventive drilling hammer. A region comprising the electromotor and a handle region of the drilling hammer are not shown. A main drive shaft extends through the indicated rotary duct 4 into the region 2 and drives a shaft 6 (in a manner not shown). The shaft 6 has a wobble plate arrangement 8 (best shown in FIG. 2) which drives a percussion mechanism 10 of the drilling hammer, and a toothed wheel 12 (only shown in FIG. 2) which rotates a drill sleeve 14.

The percussion mechanism 10 has a sleeve 18, which defines a cylindrical chamber 16 and can be moved, i.e. axially reciprocated, by the wobble plate arrangement 8 in the longitudinal direction 20 of the drill sleeve 14. The sleeve 18 is disposed inside the drill sleeve 14, concentrically thereto, and can be axially moved relative thereto. A free flight body is provided as beater 22 within the cylindrical chamber 16, which forms a pneumatic spring 24 together with the sleeve 18. When the sleeve 18 is accelerated to the left in FIG. 1 by the wobble plate arrangement 8, the beater 22 initially remains in its position due to its inertial mass, thereby forming an underpressure within the cylindrical chamber 16, which then causes delayed acceleration of the beater 22. When the sleeve 18 is moved again to the right in FIG. 1, the cylindrical chamber and the air contained therein are compressed, in particular to between 10 and 20 bar, which greatly accelerates the beater 22 towards the right and towards an intermediate piston 26. The impact surface 28 of the beater 22, facing the intermediate piston 26, strikes the intermediate piston 26 and is thereby immediately stopped, wherein the momentum is transferred to the intermediate piston 26 which subsequently strikes a tool, a drill or chisel, transferring a further momentum (percussion or hammer operation). When the intermediate piston 26 rebounds to the left in FIG. 1, it strikes the drill sleeve 14 via an intermediate elastomeric ring 30, thereby generating vibrations which are transferred to the housing of the device and which are experienced by the user as being unpleasant.

A spring means 32 of an elastomeric material 34 is provided on the outer periphery 31 of the drill sleeve 14. In the example shown, the spring means 32 or the elastomeric material 34 continuously surround the outer periphery 30 of the drill sleeve 15 in the peripheral direction. It is substantially cylindrical and has a wall thickness of between 1 and 10, in particular, 4 and 8 mm. A damping mass 36 which also has a cylindrical basic geometry, is provided radially outside on the elastomeric material 34, and in the example shown, concentrically to the drill sleeve 14. The damping mass 36 can be deflected in a resilient fashion relative to the drill sleeve 14 by the spring means 32 of elastomeric material in an axial, longitudinal direction 20 as well as in a peripheral direction. The connection between the damping mass 36 and the drill sleeve 14 basically provides six degrees of freedom due to the elastomeric material 34. The damping mass/spring system is designed such that, due to the resilient deflectable arrangement of the damping mass 36, the damping mass 36 can oscillate in a translatory and rotary direction with a respective phase which is opposite to that of the excitation oscillations acting on the drill sleeve, to thereby damp, cancel, or provide effective reduction of vibration. This eliminates two main components of the overall oscillation excitation of the drilling hammer. 

1. A motor-driven drilling hammer for driving a tool or a chuck receiving a tool, the drilling hammer comprising: a housing; a percussion and rotary drive disposed in said housing; a drill sleeve disposed in said housing and cooperating with said percussion and rotary drive and with the tool or the chuck for receiving the tool; a spring means having an elastomeric material with a wall thickness of 1 to 10 mm, said spring means connected to an outer periphery of said drill sleeve; and a damping mass held by said spring means for deflection of said damping mass relative to said drill sleeve in a peripheral and longitudinal direction of said drill sleeve due to an elasticity of said spring means, thereby effecting damping and reduction of vibrations.
 2. The drilling hammer of claim 1, wherein said elastomeric material continuously surrounds said drill sleeve in said peripheral direction and is substantially cylindrical.
 3. The drilling hammer of claim 1, wherein said elastomeric material is segmented.
 4. The drilling hammer of claim 1, wherein said elastomeric material has perforations, recesses or openings in a radial, tangential, or axial direction.
 5. The drilling hammer of claim 1, wherein said elastomeric material has a wall thickness of 4 to 8 mm.
 6. The drilling hammer of claim 1, wherein said elastomeric material has an axial extension in said longitudinal direction of said drill sleeve of 5 to 20 mm.
 7. The drilling hammer of claim 1, wherein said damping mass is substantially cylindrical.
 8. The drilling hammer of claim 1, wherein said damping mass has an axial extension in said longitudinal direction of said drill sleeve of 5 to 20 mm.
 9. The drilling hammer of claim 1, wherein said damping mass has an axial extension in said longitudinal direction of said drill sleeve, which is 3 to 8 times a wall thickness thereof.
 10. The drilling hammer of claim 1, wherein said damping mass and said spring means are designed to damp vibrations of between 30 and 100 Hz or, for small drilling hammers, between 70 to 80 Hz. 